For centuries high grade coke has been produced in so-called coke ovens by the carbonization of coal (including peat). A large percentage of such coke is used in producing iron, e.g. in blast furnaces to reduce iron ore (iron oxide) to iron. In addition, coke is also used to reduce other metal ores such as copper, etc.. However, the production of coke, in coke ovens, is a very expensive process and requires, in general, a particular type of coal which oftentimes is not located in an area near where the users of the coke made from such coal are located.
Because of these and other deficiencies in the coke oven process, it is not surprising that prior art workers have attempted to develop more efficient processes for producing coke as well as processes which can utilize Western coal which is generally considered to be non-caking (non-agglomerating) coal. In this regard, it is noted although there are many different types or ranks of coal there are generally two broad types, at least in the United States. As noted, one is so-called Western coal which is generally considered to be non-caking and the other is Eastern coal, generally considered to be a caking coal. The coke oven process has used, for the most part, the Eastern or caking coal.
Among prior art processes which have attempted to produce coke using Western type coal is that disclosed in U.S. Pat. No. 3,140,214 (Work et al.). This patent discloses a six step process for producing coke from a non-caking type coal. Included within the process are two heating steps. The first heating step is referred to in the patent as the carbonizing stage. In the carbonizing stage dried coal is heated, in a fluid bed, in the presence of oxygen at a temperature of between 800.degree. F. to 1200.degree. F. in order to remove a portion of the volatile combustible matter from the coal. Thereafter, the carbonized char is heated in a second heating step referred to in the patent as the calcining stage. In the calcining stage the carbonized char is heated to a temperature of between 1500.degree. F. to 1800.degree. F. in a fluidizing atmosphere which is free of reactive gases such as carbon dioxide and steam.
The Work et al. patent suffers from a serious disadvantage in that the gases produced in the carbonizing step and calcining step are low Btu gases (i.e. less than 150 Btu's per standard cubic foot (scf)). Such low Btu gases cannot be used to supply heat necessary to carry out the process and this is a serious, if not fatal, disadvantage.
However, up to the present time, two separate steps have been employed for, first reducing the volatile matter included in coal to produce carbonized char having 10% to 20% volatile matter and then in a separate process and a separate retorting chamber, raising the temperature to remove a portion of the remaining volatile material from the carbonized char. This two-step process required the separate handling of the exhaust gases which are produced. In addition, substantial amounts of steam are normally required to control and eliminate tar condensation from the volatile matter produced in the carbonizing step.
An important object of the present invention is to simplify the process and avoid duplication of the gas cooling, fractionation, and sulfur removal equipment, as well as reducing the need for steam formerly employed to control and eliminate tar condensation.